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Uranium-series investigations of magma-genesis and differentiation at island arc and continental settings.

机译：在岛弧和大陆环境下进行的岩浆成因和分化的铀系列研究。

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摘要

I present combined U-series, Sr-Nd-Pb isotope, and major/trace element data to constrain mass transfer processes and the timescales over which they occur beneath the Lesser Antilles and Philippine arc systems and in continental basalts.; Isotopic and element data from the Bataan and Bicol arcs, Philippines, suggest the fraction of sediment added to the mantle is limited, despite differences in sediment supply. It follows that most sediments are accreted, reside in the subarc lithosphere, or are recycled into the mantle. U-Th isotope data from the same rock suites can be explained by 230Th ingrowth models where the tectonic convergence rate controlls the extent of ( 230Th/238U) disequilibria. Thus in many cases 230Th disequilibria may not have chronologic significance and instead reflect the competing effects of U enrichment and partial melting.; The same spectrum of data from the Lesser Antilles island arc indicates ∼0.2--1.8% bulk sediment and 0.8--2.4% fluid contribution in the northern and central segments of the arc respectively. Combined with the U-Th isotope data this allows ∼100--140 ka since U enrichment of the mantle wedge.; Differentiation timescales of Taal and Mayon lavas were constrained using combined U-Th-Ra-Pa disequilibria. Ra and Pa disequilibria from Taal volcano are not "concordant", and suggest Ra data reflect open system behavior. Thus based on Pa data, differentiation from basalt to dacite is constrained at ∼30 ka. In contrast 231Pa disequilibria from Mayon volcano are constant within analytical uncertainties, and variations in 226Ra disequilibria vs. Th suggest a much shorter differentiation timescale of ∼1000--2200 yrs across the basaltic andesite compositional window.; U-Th-Ra-Pa data from three continental basalts are used to demonstrate overprinting of mantle produced 226Ra disequilibria. 231Pa disequilibria correlate with the degree of melting. However 226Ra disequilibria are constant, regardless if the lava is tholeiitic or alkali basalt. This observation could be explained by residual phlogopite/amphibole or differences in crustal storage times, yet there is no consistent evidence for either of these scenarios. The constant (226Ra/ 230Th) can be explained by crystal-melt diffusive interaction. Thus 226Ra disequilibria from melting may be overprinted, even in the simplest scenarios of melt generation and transport.
机译：我提出了结合的U系列，Sr-Nd-Pb同位素和主要/痕量元素数据，以限制传质过程及其在小安的列斯群岛和菲律宾弧系下以及大陆玄武岩中发生的时间尺度。来自菲律宾巴丹和比科尔弧的同位素和元素数据表明，尽管沉积物供应有所不同，但添加到地幔中的沉积物比例是有限的。由此可知，大多数沉积物都被吸积，存在于弧下岩石圈中或被回收到地幔中。来自相同岩石套件的U-Th同位素数据可以用230Th向内模型解释，其中构造收敛速度控制（230Th / 238U）不平衡的程度。因此，在许多情况下，230 Th失衡可能不具有年代学意义，而是反映了U富集和部分熔融的竞争作用。小安的列斯群岛弧线的数据频谱相同，分别表明弧线北部和中部的沉积物含量约为0.2--1.8％，流体贡献度约为0.8--2.4％。结合U-Th同位素数据，由于地幔楔的U富集，允许约100--140 ka。结合U-Th-Ra-Pa不平衡，限制了Taal和Mayon熔岩的分化时间尺度。塔尔火山的Ra和Pa失衡不是“一致的”，表明Ra数据反映了开放系统的行为。因此，基于Pa数据，从玄武岩到榴辉岩的分化被限制在约30 ka。相比之下，马永火山的231Pa失衡在分析不确定性范围内是恒定的，而226Ra失衡与Th的变化表明，整个玄武质安山岩组成窗口的分化时间尺度要短得多，约为1000--2200年。来自三个大陆玄武岩的U-Th-Ra-Pa数据被用来证明套印产生的226Ra不平衡。 231Pa不平衡与熔化程度相关。但是，无论熔岩是高纯玄武岩还是碱性玄武岩，226Ra失衡都是恒定的。可以用残留的金云母/闪石或地壳储存时间的差异来解释这一发现，但是对于这两种情况，都没有一致的证据。常数（226Ra / 230Th）可以通过熔体与晶体的扩散相互作用来解释。因此，即使在最简单的熔体生成和传输情况下，也可能会叠加226 Ra引起的熔解失衡。

著录项

  • 作者

    DuFrane, Scott A.;

  • 作者单位

    The University of New Mexico.;

  • 授予单位 The University of New Mexico.;
  • 学科 Geology.; Geochemistry.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 162 p.
  • 总页数 162
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;地质学;
  • 关键词

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